Eye surgeries involving ophthalmic devices usually require an incision for introducing the ophthalmic device to the target location for their intended use. Often, it is desirable to make the incision size as small as possible for fast recovery and for minimizing potential post-operational complications and side effects. In order to understand this general small incision concept, the following examples are given for the purpose of illustration, but not to limit the scope of the present invention.
Intraocular lenses (IOLs) have been used as the replacement for the crystalline lens after cataract surgery and as a phakic lens which functions together with the intact crystalline lens for correcting refractive errors. To surgically implant an intraocular lens (IOL) or phakic lens into the eye, an incision is made on the cornea. It is desirable to keep the incision size as small as possible. Implanting a traditional polymethyl methacrylate (PMMA) IOL or a PMMA phakic lens requires an incision size of about 6 mm simply because the hard PMMA lens has an optical diameter of approximately 6 mm. In order to reduce the incision size, soft materials, such as silicone or soft acrylic material have been used for lenses. A soft lens can be folded in half and then implanted into an eye with an incision size of about 3 mm. The reduction in incision size has been proven in clinical studies to reduce surgically induced astigmatism, hasten wound healing, and reduce risk of infection and/or inflammation.
Corneal inlay is an ophthalmic device surgically implanted within the cornea. A corneal inlay is designed as a lens, about 2 to 3 mm in diameter, which provides a central nearsighted vision zone for presbyopic patients. The natural cornea surrounding the inlay provides the patient with the farsighted vision. The human cornea has a thickness of approximately 0.5 mm. To implant a thin inlay lens into the cornea, the first step is to make an incision on the corneal surface without cutting through the whole corneal layer. The second step is to make a pocket within the corneal layer with the initial incision as the pocket opening. The incision should have a sufficient width so that the artificial inlay lens can be introduced into the pocket. For example, if a hard corneal inlay lens, such as a PMMA lens, is used, the minimum incision size needs to be about the same as the diameter of the PMMA lens. As with an IOL, a deformable inlay lens allows a reduced incision size and, therefore, reduced surgical trauma.
Cytomegalovirus (CMV) infection of the retina, or CMV retinitis, usually leads to blindness if untreated. CMV retinitis progresses very rapidly, particularly in HIV patients, often within weeks. One of the treatments is to introduce an anti-CMV drug inside the eye by a slow release drug delivery device through the cornea or the sclera. To implant the drug delivery device into the eye, a small incision or hole is cut through the cornea. Then the drug delivery device is pushed through the incision or the hole. For this application, it will be ideal if the drug delivery device is a hard solid rod for easy insertion. When the drug delivery device is inside the eye, it becomes soft. In addition, if the drug delivery device can be stretched into a smaller profile, it will be implanted into a reduced incision size or hole diameter. Therefore, surgical trauma is minimized.
From the examples given above, there is a need for ophthalmic devices which can be implanted into an opening which has a size smaller than the dimension of the ophthalmic device in its intended use conditions. Furthermore, the ideal ophthalmic device is a hard solid at the time of implantation so that it can be relatively easily implanted into the soft tissue opening. In addition, when warmed by the body temperature, the xe2x80x9cidealxe2x80x9d hard solid ophthalmic device can become soft and pliable for optimal tissue compatibility.
The crystalline state of polymers is defined as one that diffracts x-rays and exhibits the first order transition known as melting (L. H. Sperling, Introduction to Physical Polymer Science, John Wiley and Sons, New York, 1992). As in small molecules, crystallinity occurs when parts of a molecule arrange themselves in a regular order or arrangement. Unlike a small molecule, polymers that crystallize in the bulk state are never totally crystalline, a consequence of their long-chain nature and the chain entanglements. Even in homopolymers, there will be crystalline and amorphous regions. Polymers that have crystalline regions may be referred to as crystalline or semi-crystalline polymers. The development of crystallinity depends on the structure regularity in the polymer. An increase in non-regularity of the polymer structure decreases crystallinity of the polymer and results in a lower melting temperature. The increase in non-regularity may eventually prevent crystalline regions from forming.
The present invention utilizes crystalline polymers which provide a novel mechanism for deforming ophthalmic devices made from those polymers into a smaller profile than their initial size, at least in one dimension, so that they can be implanted into the eye through a relatively small incision. When the ophthalmic device is placed in the targeted location, it will return to its intended shape and dimension or adapt to a new configuration shaped by the tissue surrounding the ophthalmic device.
The present invention includes crystalline polymers that may be useful in the production of deformable lenses such as IOLs for cataract surgery, corneal inlays, and phakic refractive lenses for correcting ametropia, such as myopia, hyperopia, astigmatism, and presbyopia. The present invention also includes the use of crystalline polymers in ophthalmic devices which are not lens related. Such non-lens related devices may include, but are not limited to, ocular drug delivery devices, and implants for reducing intraocular pressure in glaucoma patients.
Stoy in his U.S. Pat. No. 4,731,079, issued Mar. 15, 1988, discloses a method of introducing and implanting an artificial intraocular lens to replace a surgically removed human crystalline lens through a small incision. The artificial lens material has a softening temperature in the range of about 0xc2x0 C. to about 42xc2x0 C. The method comprises the following steps: First, heat the artificial lens to a temperature higher than its softening temperature; second, deform the artificial lens into a smaller profile at least in one dimension so that it can be implanted through a small incision into the eye; third, cool down the deformed artificial lens to a temperature which is at least 5xc2x0 C. less than the softening temperature, so that the artificial lens will be frozen in the deformed configuration; fourth, implant the deformed lens into the eye through a small incision. After being warmed up by the eye temperature, the deformed lens will return to its pre-deformed shape and dimension. Stoy further teaches that preferred materials include terpolymers which contain both hydrophobic and hydrophilic monomers as well as a minor amount of monomers with at least two polymerizable double bonds. These terpolymers can be hydrated due to the presence of a desirable amount of hydrophilic monomers. The plasticizer, water in the case of the terpolymer, can lower the softening temperature of the lens material. Stoy indicates that the softening temperature may correspond to the glass transition temperature (Tg). However, Stoy is silent on whether the softening temperature can be a melting temperature (Tm). Those who are skilled in the art understand that only a crystalline polymer can have a Tm and that a crystalline polymer is typically not transparent due to the presence of crystalline structure. According to Stoy, one of the requirements for his invention is that the material must be highly transparent to visible light. Stoy further teaches that preferred polymers for use in his invention are amorphous, without a substantial amount of crystalline polymer phase being present.
MemoryLens(trademark), a commercially available implantable lens, is made from the terpolymer of methyl methacrylate (MMA), hydroxyethyl methacrylate (HEMA), and a minor amount of crosslinker. According to Dr. William J. Fishkind, MemoryLens has a composition of MMA and HEMA such that the fully hydrated lens material contains approximately 20% water and has a refractive index of 1.47. At temperatures below 25xc2x0 C., the copolymer is rigid and hard, while at temperatures above 25xc2x0 C., the copolymer begins to soften and becomes elastic. This thermoplastic characteristic of the copolymer is a function of its glass transition temperature (Tg). The MemoryLens is rolled when it is soft by increasing the temperature above its Tg, and then hardened in a fixed and rolled configuration by cooling to temperatures below its Tg. This hardened rolled lens is implanted into the eye through a small incision. Once placed inside the eye, the lens starts to become soft and relaxes to resume its pre-rolled shape. The complete shape recovery may take hours to one day to finish. Dr. Fishkind has indicated that on the first postoperative day, the folding lines will have completely resolved. (William J. Fishkind, MD, Chapter 11 xe2x80x9cORC MemoryLens(trademark)xe2x80x94A thermoplastic IOLxe2x80x9d in the book titled Foldable Intraocular Lenses by Robert G. Martin, James P. Gills, and Donald R. Sanders, SLACK Incorporated, 1993).
Copending U.S. patent application Ser. No. 09/361,729, filed Jul. 27, 1999, describes a punctal plug formed from a material which can be deformed to a convenient shape for insertion into the punctum, frozen into that shape, and which regains its original shape after insertion and warming. The optical characteristics of a punctal plug are not relevant to its operability. Further, no optical devices which are inserted into the eye through a hole or incision, such as intraocular lenses, are disclosed.
The present invention relates to an ophthalmic device suitable for implantation through an incision in the human eye (such as an ocular drug delivery device, an implant for reducing intraocular pressure, a corneal inlay, or, most preferably, an intraocular lens), made from a composition containing a crystalline or semi-crystalline polymeric material having the following properties:
(a) a glass transition temperature (Tg) in the range of from about xe2x88x92100xc2x0 C. to about 20xc2x0 C.;
(b) a melting temperature (Tm) in the range of from about 0xc2x0 C. to about 37xc2x0 C.; and
(c) wherein said glass transition temperature of the polymeric material is lower than said melting temperature for the composition.
The present invention also relates to a method for implanting into the eye, through an incision, an ophthalmic device made from a composition containing a crystalline or semi-crystalline polymeric material with a Tg in the range of from about xe2x88x92100xc2x0 C. to about 20xc2x0 C., and a Tm in the range of from about 0xc2x0 C. to about 37xc2x0 C., comprising the steps of:
(a) warming up said ophthalmic device to or above its Tm, then deforming said ophthalmic device into a deformed shape which can be implanted through an incision where the size of said incision is smaller than said ophthalmic device in its intended use condition;
(b) cooling said deformed ophthalmic device to a temperature below the Tm such that said ophthalmic device remains in said deformed shape;
(c) implanting said deformed ophthalmic device at a temperature below the Tm through said incision in the eye; and
(d) warming up said ophthalmic device to and above its Tm by the body temperature in the eye, whereupon said ophthalmic device changes into a shape suitable for its intended use.